# Tag Info

## Hot answers tagged acoustics

10

The problem is with your first calculation and also with the somewhat misleading equation that you've found. It's true that $$\frac{I_2}{I_1}=\left(\frac{d_1}{d_2}\right)^2$$ but units are important here. In that formula, $I_1$ and $I_2$ would properly be expressed as power values. To compute with decibels, which are logarithmic quantities, one would ...

5

There is both a rigorous and intuitive explanation for the dependence of the speed of propagation of mechanical waves and the density of the medium. Intuitively: You know that sound waves are longitudinal waves, resulting from a collective oscillation of the medium's molecules. When sound's propagating, it compresses and re-expands the air molecules, as one ...

5

Yes. Higher frequencies are attenuated more over distance than lower frequencies are, which has a rounding effect on the square wave as the upper harmonics are reduced. Reference Do low frequency sounds really carry longer distances?

4

The trouble is that your table, or whatever object it is, will act as a waveguide. That's because the sound waves will (partially) reflect of the wood/air surface then travel back into the table and interfere with other waves. The result is going to be hideously complicated to calculate. As Luboš says in a comment, if the thickness of the table is much less ...

4

I'll piece together some of what's been said in answers and comments in a different light. With acoustics, it pays to be very careful with units. A sound wave has a pressure $p$, and this corresponds to what I'll call it's intensity $I$. Intensity goes as the square of pressure: $$\frac{I}{I_0} = \left(\frac{p}{p_0}\right)^2.$$ Here $I_0$ is the ...

3

Almost all objects around us are electrically neutral, meaning they have no excess in negative/positive charges. When we use a plastic comb on our hair, a very small amount of negative charges start accumulating on the comb, making it negatively charged. It is important to note that it is not the friction caused by combing your hair that leads to such charge ...

3

There more sides to this scenario that you're considering. Firstly, if we are assuming that the temperature is the same at sea level and on the high mountains, then the speed of sound doesn't actually change, as a constant temperature will take care of the air pressure-density ratio. $$c = \sqrt{\kappa \frac{p}{\rho}}$$ Where $p$: static air pressure, ...

3

I'll use this answer to provide some information that's mostly orthogonal to what Phonon said. As Phonon pointed out, the speed of sound depends on temperature, not pressure. It's cold on the top of high mountains, so the speed of sound would tend to be lower. Some mechanisms for sound production have a frequency that depends on the speed of sound, and ...

3

As long as your music player is traveling with you, the music would slow down (as seen by a stationary observer). But you would not notice anything different. That's the beauty of relativity. Your "internal" clock would slow down as much as the music player's clock, and they remain relatively in synch.

2

This advertising strategy is basically using pseudoscience to get naive people to buy a product. The efficiency problem in speaker design has nothing to do with momentum transfer from the speaker to the air. That's trivial, since the mass of air a speaker moves is typically orders of magnitude less than the mass of the speaker itself. Instead, the (low ...

2

TL,DR: Magnetic coupling results in lower transmission of sound energy than physical contact Controlling what surfaces vibrate gives more control over sound generation The same benefit could be achieved with other forms of isolation (e.g. foam) but it wouldn't look as cool. It is bunk, mostly. A magnetically levitating speaker maintains a ...

2

I wanted to just raise a comment, but dont have the reputation to do so... I didnt get the same result as the python simulation, so ill just detail my thoughts below. Some assumptions (do deal with riddle as probably intended, as opposed to a real world problem): Instantaneous acceleration to new speed when we hear an alarm. An alarm is the wave-front of ...

2

In today's news - researchers at MIT did just that using high-speed camera with frame rate between 2 kHz and 6 kHz. They used some advanced filtering to detect microscopic movement of objects, but for details we will have to wait until they publish their paper.

2

The formula you use does not make any sense - you don't measure intensity of sound in dB, but the logarithm of the intensity, so you cannot multiply by the distance ratio squared.

1

I think the key here is the question of isotropy of propagation. The speed of sound in an ideal gas goes as the square root of the temperature. Another way of saying this is that the refractive index for sound waves goes as the inverse square root of temperature. Colder air has a higher refractive index. At night, it can be the case that the temperature ...

1

When two gas molecules collide their momentum will have to be conserved. Now when one molecule, with a velocity in the general direction of the propagation direction of the sound, collides head on with another molecule with the same mass, then the velocity of the other molecule will be the same as the velocity of the initial molecule travelling in the ...

1

You're question is very broad, and will probably be closed, but recently, in researching my answer to this other question, I found what may in fact be the first documented instance of someone making an informed analogy between sound and light, namely Young in his lecture to the royal society in 1803 on his observations of interference of light. I'll ...

1

The continuous stream of air that you are blowing in, it doesn't enter the pipe continuously. When the stream of air hits the hard edge in an organ pipe, it flaps in and out of it due to the difference in the density of the air outside and inside the pipe. This oscillation of the air in and out, it will be a periodic energy supply for the standing wave in ...

1

Speech sounds can be either periodic, like "aaah," or nonperiodic, like "sh." Periodic means that the pattern repeats over and over with a certain frequency. Here's a graph of sound pressure versus time for me singing the vowel "ah" at a fixed pitch: This kind of graph is referred to as a "time domain" representation of the sound, because it has time on ...

1

The energy flux of an acoustic wave is $$\vec J = \vec v p \;\;\;\;\;\;\;\;\;\;\;\;\; (1)$$ The relevant energy density to be used in these calculation is actually $p+1/2 \rho v^2$, but since we are discussing a small amplitude wave (= no shock wave), $v$ is an infinitesimal quantity; thus $1/2\rho v^2$ is lower order than $p$ (second vs. first), thus it ...

1

The surface formed by the bubble is such that its energy is minimized. Since increasing the interface between a liquid and air increases its energy due to surface tension, the bubble tends to reduce its radius, which implies that the pressure inside it must be higher than the pressure outside, and following this reasoning you may also get a quantitative ...

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